Acute neuromuscular and metabolic responses to a novel low-load combined isometric and isotonic resistance training...

This study investigated the acute physiological responses to a novel combined resistance training (CB) protocol-integrating isometric pre-exhaustion with low-load, high-velocity, short-arc isotonic contractions-and compared them with low-intensity slow training (LST) and high-load (HL) training.

Forty-eight healthy men were randomly assigned to one of three groups: LST (50% one-repetition maximum [1RM], slow tempo), HL (80% 1RM, normal tempo), or CB (40% 1RM; a 20-s isometric contraction followed by eight high-velocity, short-arc repetitions). Surface electromyography (EMG) and near-infrared spectroscopy (NIRS) of the vastus lateralis, alongside serum IGF-1 concentrations, were assessed during and following three leg-press sets.

Despite utilizing a 40% 1RM load, the CB protocol elicited mean EMG amplitudes significantly greater than LST during the final set (p = 0.009, g = 1.23). NIRS analysis demonstrated a significantly lower change in tissue oxygen saturation (ΔStO₂) in the CB group compared to HL from the initial set (p = 0.001; g = 1.19), highlighting rapid intramuscular hypoxia. Furthermore, third-set integrated EMG was significantly higher in CB than in both HL (p = 0.002, g = 1.13) and LST (p < 0.001, g = 1.63). Serum IGF-1 concentrations exhibited a significant post-exercise elevation across all groups (main effect of time: p < 0.001, η_p² = 0.712).

By concurrently demanding high neural drive and inducing profound metabolic stress, the time-efficient CB protocol provides a robust physiological stimulus despite minimal mechanical loading. This approach serves as a practical, joint-friendly alternative for populations necessitating reduced mechanical stress.

UMIN-CTR (UMIN000060486).